Dental And Medical Instruments Comprising Titanium

ABSTRACT

Endodontic instruments for use in performing root canal therapy on a tooth are disclosed. In one form, the instruments include an elongate shank having a cutting edge extending from a distal end of the shank along an axial length of the shank. The shank comprises a titanium alloy, and the shank is prepared by heat-treating the shank at a temperature above 25° C. in an atmosphere consisting essentially of a gas unreactive with the shank. In another form, the endodontic instruments have an elongate shank having a cutting edge extending from a distal end of the shank along an axial length of the shank. The shank consists essentially of a titanium alloy selected from alpha-titanium alloys, beta-titanium alloys, and alpha-beta-titanium alloys. The instruments solve the problems encountered when cleaning and enlarging a curved root canal.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication No. 60/578,091 filed Jun. 8, 2004.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to instruments used in medicine and dentistry.More particularly, the invention relates to medical and dentalinstruments such as drills, burs and files, and to endodonticinstruments such as drills, burs and files used by dentists.

2. Description of the Related Art

Endodontics or root canal therapy is the branch of dentistry that dealswith diseases of the dental pulp and associated tissues. One aspect ofendodontics comprises the treatment of infected root canals by removalof diseased pulp tissues and subsequent filling.

FIG. 1 shows a representation of a tooth to provide background. Rootcanal therapy is generally indicated for teeth having sound externalstructures but having diseased, dead or dying pulp tissues. Such teethwill generally possess intact enamel 10 and dentin 12, and will besatisfactorily engaged with the bony tissue 20, by among other things,healthy periodontal ligaments 18. In such teeth, the pulp tissue 14, andexcised portions of the root 16, should be replaced by a biocompatiblesubstitute. FIG. 1 also shows the apical foramen 22 through which bloodand nerves pass to support the pulp tissues.

One method for the preparation of a root canal for filling isrepresented by FIGS. 2 a-2 e. A tooth having a basically sound outerstructure 24 but diseased pulp 26, is cut with conventional or coateddental drill 28 creating a coronal access opening 30. A broach is usedfor gross removal of pulp material 26 from the root canal through thecoronal access opening 30. The void 32 formed is enlarged as in FIG. 2 dwith file 34, to result in a fully excavated cavity 36. Debris isremoved from this cavity by flushing and the cavity cleansed to removeall diseased tissue. The excavated canal is then ready for filling.

During this procedure, small endodontic instruments (e.g., file 34) areutilized to clean and enlarge the long narrow tapered root canals. Whilemost files perform entirely satisfactorily when cleaning and enlarging astraight root canal, problems have been encountered when using certainfiles to clean and enlarge a curved root canal. As will be understood bythose skilled in the art, a very large portion of the root canalsencountered by a practicing dentist and/or endodontist are of the curvedvariety, and thus this problem is a significant one for the profession.

When performing an operation on a curved root canal with a smallerdiameter file, the file can easily be inserted into the curved canal andwill easily bend to fit the curved shape of the canal due to theflexibility of the small diameter file. In FIG. 1 a, there is shown thefile 34 of FIG. 2 d in a bent position. The file 34 has a shank 42mounted at its proximate end 47 to a handle 43. The shank 42 may includecalibrated depth markings 45 and further includes a distal end 48. Theshank 42 includes two continuous helical flutes 51 as shown in FIG. 1 bthat extend along its lower portion. The flutes 51 define a cuttingedge. A helical land 53 is positioned between axially adjacent flutes asshown in FIG. 1 b.

While file 34 can easily bend to fit the curved shape of a canal due tothe flexibility of the small diameter shank 42, with increasingly largersizes of files, the file becomes significantly less flexible and becomesmore and more difficult to insert through the curved portion of thecanal. In some cases, the relatively inflexible file will cut only onthe inside of the curve and will not cut on the outside of the curvatureof the root canal. Thus, the problems, which occur during the therapy ofa root canal, are often the result of the basic stiffness of the files,particularly with the respect to the instruments of larger diameter.

Various solutions have been proposed to limit the problems encounteredwhen cleaning and enlarging a curved root canal with a file. Forexample, U.S. Pat. No. 4,443,193 describes a shaped endodonticinstrument that is said to solve this problem. U.S. Pat. No. 5,380,200describes an endodontic instrument having an inner core and an outershell wherein one of the cores or shell is a nickel-titanium alloy andthe other core or shell is selected from stainless steel, titanium alphaalloy, titanium beta alloy, and titanium alpha beta alloy. (Forbackground on beta-titanium, see U.S. Pat. Nos. 4,197,643; 4,892,479;4,952,236; 5,156,807; 5,232,361; 5,264,055; 5,358,586; 5,947,723;6,132,209; and 6,258,182.) U.S. Pat. No. 5,464,362 describes anendodontic instrument of a titanium alloy that is machined under certainspecific operating parameters to produce an instrument having highflexibility, high resistance to torsion breakage, and sharp cuttingedges. U.S. Pat. No. 6,315,558 proposes the use of superelastic alloyssuch as nickel-titanium that can withstand several times more strainthan conventional materials without becoming plastically deformed. Thisproperty is termed shape memory, which allows the superelastic alloy torevert back to a straight configuration even after clinical use, testingor fracture (separation).

In spite of the aforementioned advances, there remains a need formedical and dental instruments, and particularly endodontic instruments,such as drills, burs and files, that have high flexibility, have highresistance to torsion breakage, maintain shape upon fracture, canwithstand increased strain, and can hold sharp cutting edges.

SUMMARY OF THE INVENTION

The present invention overcomes the problems encountered when cleaningand enlarging a curved root canal. In one aspect, the invention providesan endodontic instrument for use in performing root canal therapy on atooth. The instrument includes an elongate shank having a cutting edgeextending from a distal end of the shank along an axial length of theshank. The shank comprises a titanium alloy, and the shank is preparedby heat-treating the shank at a temperature above 25° C. in anatmosphere consisting essentially of a gas unreactive with the shank.The shank has high flexibility, high resistance to torsion breakage,maintains shape upon fracture, can withstand increased strain, and canhold sharp cutting edges. Thus, it solves the problems encountered whencleaning and enlarging a curved root canal.

In another aspect, the invention provides an endodontic instrument foruse in performing root canal therapy on a tooth. The instrument has anelongate shank having a cutting edge extending from a distal end of theshank along an axial length of the shank. The shank consists essentiallyof a titanium alloy selected from alpha-titanium alloys, beta-titaniumalloys, and alpha-beta-titanium alloys. The shank avoids the use ofcomplex two material systems that are expensive to produce and are proneto delamination of the materials. This version of the invention alsosolves the problems encountered when cleaning and enlarging a curvedroot canal.

These and other features, aspects, and advantages of the presentinvention will become better understood upon consideration of thefollowing detailed description, drawings, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a tooth.

FIG. 1 a is a side elevational view of an endodontic instrument.

FIG. 1 b is a partial detailed view of the shank of the endodonticinstrument shown in FIG. 1 a.

FIGS. 2 a-2 e represent a prior art procedure for preparing a tooth forendodontic restoration.

FIG. 3 is a graph showing the results of a study of torsion (M_(t))reported in g·cm performed in accordance with “ISO Standard 3630-1Dentistry—Root-canal instruments—Part 1: General requirements” and“ANSI/ADA Specification No. 28, Endodontic files and reamers” foruntreated (Control) files, heat-treated files (TT), and titanium nitridecoated files (Ti—N).

FIG. 4 is a graph showing the results of a study of torsion (A_(t))reported in degrees of deflection performed in accordance with “ISOStandard 3630-1 Dentistry—Root-canal instruments—Part 1: Generalrequirements” and “ANSI/ADA Specification No. 28, Endodontic files andreamers” for untreated (Control) files, heat-treated files (TT), andtitanium nitride coated files (Ti—N).

FIG. 5 is a graph showing the results of a study of maximum torque at45° of flexion (Mf) reported in g-cm performed in accordance with “ISOStandard 3630-1 Dentistry—Root-canal instruments—Part 1: Generalrequirements” and “ANSI/ADA Specification No. 28, Endodontic files andreamers” for untreated (Control) files, heat-treated files (TT), andtitanium nitride coated files (Ti—N).

FIG. 6 is a graph showing the results of a study of angle of permanentdeformation after the flexion test (ADP) reported in degrees ofdeflection performed in accordance with “ISO Standard 3630-1Dentistry—Root-canal instruments—Part 1: General requirements” and“ANSI/ADA Specification No. 28, Endodontic files and reamers” foruntreated (Control) files, heat-treated files (TT), and titanium nitridecoated files (Ti—N).

FIG. 7 is a graph showing the results of a study of fatigue reported incycles (revolutions) to failure for untreated (Control) files,heat-treated files (TT), and titanium nitride coated files (Ti—N). Thisstudy was performed in accordance with the “ISO Standard 3630-2 Dentalroot-canal instruments—Part 2: Enlargers” and “ANSI/ADA SpecificationNo. 95, for Root canal enlargers”.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the invention provides an improved endodonticinstrument for use in performing root canal therapy on a tooth. Thisembodiment of the invention is an endodontic instrument as shown in FIG.1 a that includes an elongate shank 42 mounted at its proximate end 47to a handle 43. The shank 42 may be about 30 millimeters long. Theproximate end 47 may have a diameter of about 0.5 to about 1.6millimeters. The shank 42 may include calibrated depth markings 45 andfurther includes a distal end 48. The shank 42 includes two continuoushelical flutes 51 as shown in FIG. 1 b that extend along its lowerportion. The flutes 51 define a cutting edge. A helical land 53 ispositioned between axially adjacent flutes as shown in FIG. 1 b.

The shank 42 comprises a titanium alloy, and is prepared byheat-treating the shank at a temperature above 25° C. in an atmosphereconsisting essentially of a gas unreactive with the shank. Preferably,the temperature is from 400° C. up to but not equal to the melting pointof the titanium alloy, and most preferably, the temperature is from 475°C. to 525° C. Preferably, the gas is selected from the group consistingof helium, neon, argon, krypton, xenon, and radon. Most preferably, thegas is argon. In one example embodiment, the shank is heat-treated forapproximately 1 to 2 hours. In another example embodiment, the shank isheat-treated at 500° C. for 75 minutes. However, other temperatures aresuitable as they are dependent on the time period selected for heatexposure.

The titanium alloy may be selected from alpha-titanium alloys,beta-titanium alloys, alpha-beta-titanium alloys, and nickel-titaniumalloys. Non-limiting examples of alpha-titanium alloys, beta-titaniumalloys, alpha-beta-titanium alloys for use in this embodiment of theinvention are: Ti-5Al-2.5Sn alpha alloy; Ti-5Al-2.5Sn-ELI (low O₂) alphaalloy; Ti-3Al-2.5V alpha alloy; Ti-5Al-5Zr-5Sn alpha alloy;Ti-6Al-2Cb-1Ta-0.8Mo alpha alloy; Ti-5Al-5Sn-2Zr-2Mo-0.25Si near alphaalloy; Ti-6Al-2Nb-1Ta-1Mo near alpha alloy; Ti-8Al-1Mo-1V near alphaalloy; Ti-6Al-2Sn-4Zr-2Mo near alpha alloy;Ti-6Al-2Sn-1.5Zr-1Mo-0.35Bi-0.1Si near alpha alloy;Ti-2.25-Al-11Sn-5Zr-1Mo-0.2Si near alpha alloy; Ti-3Al-2.5V alpha-betaalloy; Ti-10V-2Fe-3Al alpha-beta alloy; Ti-5Al-2Sn-2Zr-4Mo-4Cralpha-beta alloy; Ti-6Al-2Sn-4Zr-6Mo alpha-beta alloy; Ti-4Al-4Mnalpha-beta alloy; Ti-6Al-2Sn-2Zr-2Mo-2Cr-0.25Si alpha-beta alloy;Ti-4Al-3Mo-1V alpha-beta alloy; Ti-6Al-2Sn-4Zr-6Mo alpha-beta alloy;Ti-11Sn-5Zr-2Al-1Mo alpha-beta alloy; Ti-6Al-4V alpha-beta alloy;Ti-6Al-4V-ELI (low O₂) alpha-beta alloy; Ti-6Al-6V-2Sn-0.75Cu alpha-betaalloy; Ti-7Al-4Mo alpha-beta alloy; Ti-6Al-2Sn-4Zr-2Mo alpha-beta alloy;Ti-5Al-1.5Fe-1.5Cr-1.5Mo alpha-beta alloy; Ti-8Mn alpha-beta alloy;Ti-8Mo-8V-2Fe-3Al beta alloy; Ti-11.5Mo-6Zr-4.5Sn beta alloy;Ti-3Al-8V-6Cr-4Mo-4Zr beta alloy; and Ti-3Al-13V-11Cr beta alloy (thenumbers being percent by weight). An example, nickel-titanium alloyincludes 54-57 weight percent nickel and 43-46 weight percent titanium.Preferably, the titanium alloy used for the shank includes 54-57 weightpercent nickel and 43-46 weight percent titanium and is commerciallyavailable as Nitinol 55. Thus, most preferably, the shank consistsessentially of 54-57 weight percent nickel and 43-46 weight percenttitanium thereby avoiding the inclusion of elements that affect thesuperelastic properties of the alloy.

Another embodiment of the invention provides an improved endodonticinstrument for use in performing root canal therapy on a tooth. Thisembodiment of the invention is an endodontic instrument as shown in FIG.1 a that includes an elongate shank 42 mounted at its proximate end 47to a handle 43. The shank 42 may be about 30 millimeters long. Theproximate end 47 may have a diameter of about 0.5 to about 1.6millimeters. The shank 42 may include calibrated depth markings 45 andfurther includes a distal end 48. The shank 42 includes two continuoushelical flutes 51 as shown in FIG. 1 b, which extend along its lowerportion. The flutes 51 define a cutting edge. A helical land 53 ispositioned between axially adjacent flutes as shown in FIG. 1 b. Theendodontic instrument is fabricated solely from an alpha-titanium alloy,a beta-titanium alloy, or an alpha-beta-titanium alloy to avoid theproblems associated with multiple alloy systems.

Non-limiting examples of alpha-titanium alloys, beta-titanium alloys,alpha-beta-titanium alloys for use in this embodiment of the inventionare: Ti-5Al-2.5Sn alpha alloy; Ti-5Al-2.5Sn-ELI (low O₂) alpha alloy;Ti-3Al-2.5V alpha alloy; Ti-5Al-5Zr-5Sn alpha alloy;Ti-6Al-2Cb-1Ta-0.8Mo alpha alloy; Ti-5Al-5Sn-2Zr-2Mo-0.25Si near alphaalloy; Ti-6Al-2Nb-1Ta-1Mo near alpha alloy; Ti-8Al-1Mo-1V near alphaalloy; Ti-6Al-2Sn-4Zr-2Mo near alpha alloy;Ti-6Al-2Sn-1.5Zr-1Mo-0.35Bi-0.1Si near alpha alloy;Ti-2.25-Al-11Sn-5Zr-1Mo-0.2Si near alpha alloy; Ti-3Al-2.5V alpha-betaalloy; Ti-10V-2Fe-3Al alpha-beta alloy; Ti-5Al-2Sn-2Zr-4Mo-4Cralpha-beta alloy; Ti-6Al-2Sn-4Zr-6Mo alpha-beta alloy; Ti-4Al-4Mnalpha-beta alloy; Ti-6Al-2Sn-2Zr-2Mo-2Cr-0.25Si alpha-beta alloy;Ti-4Al-3Mo-1V alpha-beta alloy; Ti-6Al-2Sn-4Zr-6Mo alpha-beta alloy;Ti-11Sn-5Zr-2A-1Mo alpha-beta alloy; Ti-6Al-4V alpha-beta alloy;Ti-6Al-4V-ELI (low O₂) alpha-beta alloy; Ti-6Al-6V-2Sn-0.75Cu alpha-betaalloy; Ti-7Al-4Mo alpha-beta alloy; Ti-6Al-2Sn-4Zr-2Mo alpha-beta alloy;Ti-5Al-1.5Fe-1.5Cr-1.5Mo alpha-beta alloy; Ti-8Mn alpha-beta alloy;Ti-8Mo-8V-2Fe-3Al beta alloy; Ti-11.5Mo-6Zr-4.5Sn beta alloy;Ti-3Al-8V-6Cr-4Mo-4Zr beta alloy; and Ti-3Al-13V-11Cr beta alloy (thenumbers being percent by weight). These alloys of titanium include phasestabilizing amounts of a metal selected from molybdenum, tin, bismuth,tantalum, vanadium, zirconium, niobium, chromium, cobalt, nickel,manganese, iron, aluminum and lanthanum. An endodontic instrumentaccording to this embodiment of the invention has improved sharpness,cutting ability, and instrument longevity compared to instrumentsfabricated from untreated nickel-titanium. Alpha-titanium, beta-titaniumand alpha-beta-titanium are superior because they are harder and hencewill hold an edge better and still maintain near the flexibility ofnickel-titanium to negotiate curved canals. These alpha-titanium,beta-titanium and alpha-beta-titanium instruments may include medical,dental and endodontic instruments (both hand and engine driven), cuttingburs (drills), and enlarging instruments including hand, mechanical androtary.

Present medical and dental practice entails cutting of hard tissues suchas bone or teeth with instruments manufactured of carbide steel,stainless steel and nickel-titanium. Present endodontic practice entailsthe preparation, cleaning, and shaping of root canals in teeth utilizingcarbide steel, stainless steel and nickel-titanium instruments for hand,mechanical and rotary applications. This version of the invention woulduse an alpha-titanium alloy, a beta-titanium alloy, or analpha-beta-titanium alloy to fabricate these instruments. It may becoated (as described below) or uncoated. Today a growing number ofphysicians and dentists (endodontists) are utilizing engine drivendrills and files with various names and applications. This aspect of thepresent invention pertains to the fabrication of these cuttinginstruments such as drills and files solely from an alpha-titaniumalloy, a beta-titanium alloy, or an alpha-beta-titanium alloy to producea sharper cutting edge that should provide for better cutting or asmooth finished surface. This includes instrumentation that willfacilitate the cleaning and sealing of the root canal system. Inaddition, a coating or heat-treatment may relieve stress in theinstrument to allow it to withstand more torque, rotate through a largerangle of deflection, change the handling properties, or visually exhibita near failure of the instrument. This aspect of the invention relatesto all drills, burs, files, and instruments used in medicine anddentistry.

In another aspect, the present invention provides for coating andoptionally thereafter heat-treating dental and medical instrumentsincluding the coatings to maintain and/or improve their sharpness,cutting ability, and/or instrument longevity. Such an instrument may bemanufactured from nickel-titanium, an alpha-titanium alloy, abeta-titanium alloy, or an alpha-beta-titanium alloy, stainless steel,carbide steel, as well as other materials. These instruments may beelectropolished before or after coating or heat-treating. Theseinstruments will include medical, dental and endodontic instruments(both hand and engine driven), cutting burs (drills), and enlarginginstruments including hand, mechanical and rotary.

The coating processes may include but not limited to the followingprocesses: composite electroless plating (see, e.g., U.S. Pat. Nos.4,820,547; 4,997,686; 5,145,517; 5,300,330; 5,863,616; and 6,306,466);chemical vapor deposition (see, e.g., U.S. Pat. No. 4,814,294);microwave deposition (see, e.g., U.S. Pat. No. 4,859,493); laserablation process (see, e.g., U.S. Pat. No. 5,299,937); ion beam assisteddeposition (see, e.g., U.S. Pat. No. 5,725,573); physical vapordeposition (see, e.g., U.S. Pat. Nos. 4,670,024, 4,776,863, 4,984,940,and 5,545,490); Molybdenum Disulfide Coating (MoS₂) (see, e.g., U.S.Pat. No. 5,037,516 or SAE Standard AMS2526); electropolishing; coatingsincluding titanium nitride and titanium aluminum nitride commerciallyavailable under the trademark Firex™; coatings such as titanium nitride(TiN), titanium carbonitride (TiCN), titanium aluminum nitride (TiAlN),aluminum titanium nitride (AlTiN); or multiple coatings or combinationsof coatings.

As detailed above, present medical and dental practice entails cuttingof hard tissues such as bone or teeth with instruments manufactured ofcarbide steel, stainless steel and nickel-titanium. Present endodonticpractice entails the preparation, cleaning, and shaping of root canalsin teeth utilizing carbide steel, stainless steel and nickel-titanium.These can be manufactured as hand, mechanical and rotary instruments.Today a growing number of physicians and dentists (endodontists) areutilizing engine driven drills and files with various names andapplications. This aspect of the present invention pertains to theapplication of coatings and optionally heat-treatment to cuttinginstruments such as drills and files to produce a sharper cutting edgeand a higher resistance to heat degradation that should provide forbetter cutting, a smooth surface and/or different metallurgicalproperties than the material from which it was manufactured. Thisincludes instrumentation that will facilitate the cleaning and sealingof the root canal system. In addition, a heat-treatment separatelyapplied or as utilized in the coating process may relieve stress in theinstrument which should allow for more instrument longevity by theability to withstand more torque, rotate through a larger angle ofdeflection, change the handling properties, remove shape memory orvisually exhibit a near failure of the instrument. This aspect of theinvention relates to all drills, burs, files, and instruments used inmedicine and dentistry.

One example process of this aspect of the present invention for suchinstruments is a titanium nitride coating. This coating process is donewith physical vapor deposition with an inherent heat-treatment. Anotherprocess is a multilayer process utilizing a titanium nitride coating andthen a titanium aluminum nitride coating. This last coating process iscommercially available under the trademark FIREX™.

Another example process of this aspect of the present invention for suchinstruments is a metal or metal alloy coating incorporating particulatematter. One process to produce such a coating to an instrument includescontacting the surface of the instrument with a stable electrolessmetallizing bath comprising a metal salt, an electroless reducing agent,a complexing agent, an electroless plating stabilizer, a quantity ofparticulate matter which is essentially insoluble or sparingly solublein the metallizing bath, and a particulate matter stabilizer, andmaintaining the particulate matter in suspension in the metallizing bathduring the metallizing of the instrument for a time sufficient toproduce a metallic coating with the particulate matter dispersed.

EXAMPLES

The following Examples have been presented in order to furtherillustrate the invention and are not intended to limit the invention inany way.

Example 1

Thirty ISO size SX files, thirty ISO size S1 files, thirty ISO size S2files, thirty ISO size F1 files, thirty ISO size F2 files and thirty ISOsize F3 files were used in a study of torsion (M_(t)) reported in g·cmperformed in accordance with “ISO Standard 3630-1 Dentistry—Root-canalinstruments—Part 1: General requirements” and “ANSI/ADA SpecificationNo. 28, Endodontic files and reamers”. The results are shown in FIG. 3.The files were made from a titanium alloy comprising 54-57 weightpercent nickel and 43-46 weight percent titanium, and included anelongate shank having a cutting edge extending from a distal end of theshank along an axial length of the shank. Ten of each ISO size wereuntreated (Control) files. Ten of each ISO size were heat-treated in afurnace in an argon atmosphere at 500° C. for 75 minutes. These arelabeled “TT” in FIG. 3. Ten of each ISO size were coated with titaniumnitride using physical vapor deposition with an inherent heat-treatment.These are labeled “Ti—N” in FIG. 3. M_(t) was determined for each of thethirty files in each size, and the mean and standard deviation for eachgroup (Control, TT, Ti—N) of ten files were calculated. The ten files inall but one size that were heat-treated in a furnace in an argonatmosphere at 500° C. for 75 minutes showed the best result with thehighest M_(t).

Example 2

Thirty ISO size SX files, thirty ISO size S1 files, thirty ISO size S2files, thirty ISO size F1 files, thirty ISO size F2 files and thirty ISOsize F3 files were used in a study of torsion (A_(t)) reported indegrees of deflection performed in accordance with “ISO Standard 3630-1Dentistry—Root-canal instruments—Part 1: General requirements” and“ANSI/ADA Specification No. 28, Endodontic files and reamers”. Theresults are shown in FIG. 4. The files were made from a titanium alloycomprising 54-57 weight percent nickel and 43-46 weight percenttitanium, and included an elongate shank having a cutting edge extendingfrom a distal end of the shank along an axial length of the shank. Tenof each ISO size were untreated (Control) files. Ten of each ISO sizewere heat-treated in a furnace in an argon atmosphere at 500° C. for 75minutes. These are labeled “TT” in FIG. 4. Ten of each ISO size werecoated with titanium nitride using physical vapor deposition with aninherent heat-treatment. These are labeled “Ti—N” in FIG. 4. A_(t) wasdetermined for each of the thirty files in each size, and the mean andstandard deviation for each group (Control, TT, Ti—N) of ten files werecalculated. The ten files in each size that were heat-treated in afurnace in an argon atmosphere at 500° C. for 75 minutes showed the bestresults with the highest A_(t).

Example 3

Thirty ISO size SX files, thirty ISO size S1 files, thirty ISO size S2files, thirty ISO size F1 files, thirty ISO size F2 files and thirty ISOsize F3 files were used in a study of maximum torque at 45° of flexion(M_(f)) reported in g·cm performed in accordance with “ISO Standard3630-1 Dentistry—Root-canal instruments—Part 1: General requirements”and “ANSI/ADA Specification No. 28, Endodontic files and reamers”. Theshank is held in a torque meter, flexed at an angle of 45°, and thentorque is measured. The results are shown in FIG. 5. The files were madefrom a titanium alloy comprising 54-57 weight percent nickel and 43-46weight percent titanium, and included an elongate shank having a cuttingedge extending from a distal end of the shank along an axial length ofthe shank. Ten of each ISO size were untreated (Control) files. Ten ofeach ISO size were heat-treated in a furnace in an argon atmosphere at500° C. for 75 minutes. These are labeled “TT” in FIG. 5. Ten of eachISO size were coated with titanium nitride using physical vapordeposition with an inherent heat-treatment. These are labeled “Ti—N” inFIG. 5. Mf was determined for each of the thirty files in each size, andthe mean and standard deviation for each group (Control, TT, Ti—N) often files were calculated. It can be seen that the heat-treated files ineach size impart less torque when bent and appear to have higherflexibility than untreated (control) files.

Example 4

Thirty ISO size SX files, thirty ISO size S1 files, thirty ISO size S2files, thirty ISO size F1 files, thirty ISO size F2 files and thirty ISOsize F3 files were used in a study of angle of permanent deformationafter the flexion test (ADP) reported in degrees of deflection performedin accordance with “ISO Standard 3630-1 Dentistry—Root-canalinstruments—Part 1: General requirements” and “ANSI/ADA SpecificationNo. 28, Endodontic files and reamers”. The results are shown in FIG. 6.The files were made from a titanium alloy comprising 54-57 weightpercent nickel and 43-46 weight percent titanium, and included anelongate shank having a cutting edge extending from a distal end of theshank along an axial length of the shank. Ten of each ISO size wereuntreated (Control) files. Ten of each ISO size were heat-treated in afurnace in an argon atmosphere at 500° C. for 75 minutes. These arelabeled “TT” in FIG. 6. Ten of each ISO size were coated with titaniumnitride using physical vapor deposition with an inherent heat-treatment.These are labeled “Ti—N” in FIG. 6. ADP was determined for each of thethirty files in each size, and the mean and standard deviation for eachgroup (Control, TT, Ti—N) of ten files were calculated. The ten files ineach size that were heat-treated in a furnace in an argon atmosphere at500° C. for 75 minutes showed the highest ADP. Thus, the heat-treatedfiles significantly maintain the acquired (test deformed) shape ratherthan the shape memory exhibited in the untreated control(nickel-titanium instruments).

Example 5

Six groups of thirty ISO size SX, S1, S2, F1, F2 and F3 files were usedin a study of the fatigue reported in cycles (revolutions) to failureperformed in accordance with the “ISO Standard 3630-2 Dental root-canalinstruments—Part 2: Enlargers” and “ANSI/ADA Specification No. 95, forRoot canal enlargers”. The results are shown in FIG. 7. The files weremade from a titanium alloy comprising 54-57 weight percent nickel and43-46 weight percent titanium, and included an elongate shank having acutting edge extending from a distal end of the shank along an axiallength of the shank. Ten files of each ISO size were untreated (Control)files. Ten files of each ISO size were heat-treated in a furnace in anargon atmosphere at 500° C. for 75 minutes. These are labeled “TT” inFIG. 7. Ten files of each ISO size were coated with titanium nitrideusing physical vapor deposition with an inherent heat-treatment. Theseare labeled “Ti—N” in FIG. 7. Fatigue cycles were determined for each ofthe files in each size, and the mean and standard deviation for eachgroup (Control, TT, Ti—N) of the six file sizes were calculated. The tenfiles in all but one size that were heat-treated in a furnace in anargon atmosphere at 500° C. for 75 minutes showed the best result withthe highest fatigue cycles (revolutions) to failure.

The Examples show that heat-treated files (TT) exhibit higher resistanceto torsion breakage, can withstand increased strain, have higherflexibility, have increased fatigue life and maintain any acquired shapeupon fracture better when compared to untreated (Control) files. Thus,the invention provides medical and dental instruments, and particularlyendodontic instruments, such as drills, burs and files, that have highresistance to torsion breakage, maintain shape upon fracture, canwithstand increased strain, and can hold sharp cutting edges such thatthe instruments overcome the problems encountered when cleaning andenlarging a curved root canal.

Although the present invention has been described in considerable detailwith reference to certain embodiments, one skilled in the art willappreciate that the present invention can be practiced by other than thedescribed embodiments, which have been presented for purposes ofillustration and not of limitation. For example, while the presentinvention finds particular utility in the field of endodonticinstruments, the invention is also useful in other medical and dentalinstruments used in creating or enlarging an opening. Therefore, thescope of the appended claims should not be limited to the description ofthe embodiments contained herein.

1. An endodontic instrument for use in performing root canal therapy ona tooth, the instrument comprising: an elongate shank having a cuttingedge extending from a distal end of the shank along an axial length ofthe shank, wherein the shank comprises a titanium alloy, and wherein theshank is prepared by heat-treating the shank at a temperature above 25°C. in an atmosphere consisting essentially of a gas unreactive with theshank.
 2. The instrument of claim 1 wherein: the gas is selected fromthe group consisting of helium, neon, argon, krypton, xenon, and radon.3. The instrument of claim 1 wherein: the temperature is from 400° C. upto but not equal to the melting point of the titanium alloy.
 4. Theinstrument of claim 1 wherein: the temperature is from 475° C. to 525°C.
 5. The instrument of claim 1 wherein: the shank is heat-treated for 1to 2 hours.
 6. The instrument of claim 1 wherein: the titanium alloy isselected from alpha-titanium alloys, beta-titanium alloys,alpha-beta-titanium alloys, and nickel-titanium alloys.
 7. Theinstrument of claim 1 wherein: the titanium alloy comprises 54-57 weightpercent nickel and 43-46 weight percent titanium.
 8. The instrument ofclaim 1 wherein: the titanium alloy comprises 54-57 weight percentnickel and 43-46 weight percent titanium, the gas is selected from thegroup consisting of helium, neon, argon, krypton, xenon, and radon, thetemperature is from 475° C. to 525° C., and the shank is heat-treatedfor 1 to 2 hours.
 9. The instrument of claim 1 wherein: the shankconsists essentially of a titanium alloy comprising 54-57 weight percentnickel and 43-46 weight percent titanium, the gas is argon, thetemperature is 500° C., and the shank is heat-treated for 1 to 2 hours.10. The instrument of claim 1 wherein: the cutting edge is formed byhelical flutes in the shank.
 11. The instrument of claim 1 wherein: theshank has an angle greater than 10 degrees of permanent deformationafter torque at 45° of flexion.
 12. The instrument of claim 1 wherein:the shank has a diameter of 0.5 to 1.6 millimeters.
 13. An endodonticinstrument for use in performing root canal therapy on a tooth, theinstrument comprising: an elongate shank having helical flutes defininga cutting edge extending from a distal end of the shank along an axiallength of the shank, wherein the shank consists essentially of atitanium alloy comprising 54-57 weight percent nickel and 43-46 weightpercent titanium, and wherein the shank is prepared by heat-treating theshank at a temperature from 475° C. to 525° C. in an atmosphereconsisting essentially of argon gas.
 14. The instrument of claim 13wherein: the shank has a diameter of 0.5 to 1.6 millimeters.
 15. Amethod for creating or enlarging an opening in a tooth of a patientundergoing root canal therapy, the method comprising: creating orenlarging the opening using an instrument according to claim
 1. 16. Anendodontic instrument for use in performing root canal therapy on atooth, the instrument comprising: an elongate shank having a cuttingedge extending from a distal end of the shank along an axial length ofthe shank, wherein the shank consists essentially of a titanium alloyselected from alpha-titanium alloys, beta-titanium alloys, andalpha-beta-titanium alloys.
 17. The instrument of claim 16 wherein: thecutting edge is formed by helical flutes in the shank.
 18. Theinstrument of claim 16 wherein: the shank has a diameter of 0.5 to 1.6millimeters.
 19. A method for creating or enlarging an opening in atooth of a patient undergoing root canal therapy, the method comprising:creating or enlarging the opening using an instrument according to claim16.
 20. A method for creating or enlarging an opening in a tooth of apatient undergoing root canal therapy, the method comprising: creatingor enlarging the opening using an instrument according to claim 13.